Resistance to metalaxyl-M and cymoxanil in a dominant clonal lineage of Phytophthora infestans in Huánuco, Peru, an area of continuous potato production

Abstract

Fifty-eight isolates of Phytophthora infestans were evaluated in vitro and on detached leaves of potato for their sensitivities to metalaxyl-M and cymoxanil. The isolates belonged to the clonal lineage, EC-1, which is dominant on potato in Peru and Ecuador. All isolates were collected in Huánuco, Peru, an area of year-round potato production, where the potential for development of fungicide resistance is high. All isolates were resistant to metalaxyl-M, with in vitro EC 50 values ranging from 468.30-813.57 mg l −1 . In contrast, we found no evidence for resistance to cymoxanil for which in vitro EC 50 values ranged from 0.03-1.11 mg l −1 . Resistance to each fungicide was also evaluated for five isolates in a detached leaf assay in which the fungicide was sprayed on the leaf surface prior to inoculation. With metalaxyl-M, the range of EC 50 values was 158.85-828.29 mg l −1 , similar to that for the in vitro assay. For cymoxanil, EC 50 values ranged from 1.41 to 2.31 mg l −1 , which was higher than in the in vitro assay but still two orders of magnitude lower than the concentration applied by farmers in the field.

Conditional QTL underlying resistance to late blight in a diploid potato population

“…Our experiments were planted later in the season than local potato crops to ensure the build up of inoculation. Oxapampa and Comas are areas where disease can remain present all year such that inoculum in varying levels is available all the time (Pérez et al 2009). …”

The CAZyome of Phytophthora spp.: A comprehensive analysis of the gene complement coding for carbohydrate-active enzymes in species of the genus Phytophthora

“…Currently, no single strategy is successful at controlling late blight; hence, integrated management is presently the most reliable approach for disease control [ 2 ]. The apparent resilience of P. infestans to typical control measures such as the fungicide metalaxyl [ 3 - 7 ] or new approaches such as the use of resistance genes [ 8 - 10 ] was observed especially after the A2 mating type became more prevalent, facilitating sexual reproduction and recombination, and leading to an increase of the genetic diversity of P. infestans populations [ 11 ]. The ability to overcome control alternatives that had been successful previously is probably due to P. infestans' genome plasticity, as evidenced by the presence of multiple isozyme genotypes in sexual populations [ 12 ].…”

Mating type, mefenoxam sensitivity, and pathotype diversity in Phytophthora infestans isolates from tomato in Brazil

“…In a recent survey carried out in Peru, all P. infestans isolates tested were resistant to metalaxyl-m (Pérez et al, 2009). The isolates belonged to the clonal lineage EC-1, a recently introduced one which is dominant on potato in Peru and Ecuador.…”

“…Selection of fungicide-insensitive individuals in populations of plant-pathogenic fungi is a common event and is reported more frequently for systemic fungicides. There are several reports of resistance to metalaxyl in P. infestans (Gisi & Cohen, 1996;Reis et al, 2005;Pérez et al, 2009). Thus, monitoring pathogen insensitivity, especially to systemic fungicides, is an important component of disease management (Gisi & Cohen, 1996).…”